Function copy_len_floor 

pub fn copy_len_floor(value: &AnyValue<'_>, stop: usize) -> usize

At least how many bytes copy_text writes for value, counted only until the count passes stop: a copy can be refused at a cap before it is formatted, and a million-item list is not walked to learn that it is over. Text is its length and bytes their base64; a list or struct is counted from its punctuation and leaves, each at its shortest JSON.